Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize SSL devices (e.g., light emitting diodes (LEDs)) for background illumination. SSL devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. FIGS. 1A and 1B are cross-sectional and plan views of a conventional SSL device 10, respectively. As shown in FIGS. 1A and 1B, the SSL device 10 includes an LED structure 11 having N-type gallium nitride (GaN) 14, GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 16, and P-type GaN 18. The SSL device 10 also includes a first contact 20 proximate the N-type GaN 14 and a second contact 22 proximate the P-type GaN 18. The first contact 20 includes a plurality of contact fingers 21 (three are shown for illustration purposes) coupled to one another by a cross member 23. The second contact 22 includes a sheet-like structure.
In operation, a continuous or pulsed electrical voltage is applied between the first and second contacts 20 and 22. In response, an electrical current flows from the first contact 20, through the N-type GaN 14, the GaN/InGaN MQWs 16, and the P-type GaN 18, to the second contact 22. The GaN/InGaN MQWs 16 convert a portion of the electrical energy into light, and the light is extracted from the N-type GaN 14 of the SSL devices 10 for illumination, signage, and/or other suitable purposes.
The SSL device 10, however, may have low light extraction efficiencies. According to conventional techniques, the first and second contacts 20 and 22 typically include aluminum, copper, silver, and/or other non-transparent conductive materials. As a result, light generated in areas corresponding to the contact fingers 21 and cross member 23 can be difficult to extract. On the other hand, as discussed in more detail below, the areas of the GaN/InGaN MQWs 16 directly between the second contact 22 and the contact fingers 21 and cross member 23 of the first contact 20 produce the highest light intensity in the SSL device 10. As a result, a large portion of the light generated in the SSL device 10 may be blocked by the first contact 20. Accordingly, several improvements in increasing light extraction efficiency in SSL devices may be desirable.